AP600 Reactor Coolant Pumps

The AP600 reactor coolant system (RCS) employs high inertia, high reliability, low maintenance canned motor pumps for circulating primary reactor coolant through the reactor core, piping, and steam generators. Two pumps are mounted directly in the channelhead of each steam generator. This allows the pumps and steam generator to use the same structural support, greatly simplifying the support system and providing more space for pump and steam generator maintenance. The combined steam generator/pump vertical support is a single column extending from the floor to the bottom of the channelhead.

Large Operating Experience Base

Inverted canned motors have been in operation for over 25 years in fossil boiler circulation systems with better operating reliability than upright units because the motor cavity is self-venting into the pump casing, avoiding the potential for gas pockets in the bearing and water regions. Approximately 1300 units have been built and placed into service. The pumps are integrated into the steam generator channelhead in the inverted position.

The advantages of this pump design are significant. The auxiliary fluid systems needed to support a canned motor pump are much less complex than those needed for a shaft seal type pump. The canned motor pump is more tolerant of off-design conditions than shaft seal pumps, and inherently reduces the potential for small loss-of-coolant accidents (LOCAs) by eliminating the shaft seal. The integration of the pump suction into the bottom of the steam generator channelhead eliminates the crossover leg of coolant loop piping; reduces the loop pressure drop; simplifies the foundation and support system for the steam generator, pumps, and piping; and eliminates a potential of core uncovery during a small LOCA.